Certain known pipeline laying vessels are normally configured to construct a pipeline on board, and release the pipeline gradually into a body of water. The pipeline is made of pipe sections joined together on an assembly line, and release of the pipeline is controlled by one or more tensioning devices configured to grip the pipeline on opposite sides, selectively move the pipeline forward in a controlled manner, and retain the pipeline in a given position with respect to the laying vessel.
When the pipeline is completed or laying is interrupted by bad weather, the pipeline must be abandoned on the bed of the body of water. And, when the abandoned pipeline is not completed, the pipeline must be recovered on board the laying vessel to continue construction.
In certain instances, the pipeline is abandoned and recovered by connecting the end of the pipeline to a rope connected to a hauling machine, normally a winch, which unwinds/winds the rope to abandon/recover the pipeline. When abandoning the pipeline in the water, the end is first sealed to prevent the pipeline from flooding.
The maximum load capacity of the hauling machine is normally configured to withstand the maximum possible load exerted by the pipeline on the rope, plus a certain margin of safety. Flooding of the pipeline is extremely rare, but cannot be predicted or prevented beforehand. The pipeline, for example, may flood as a result of cracks produced in the pipeline wall by excessive bending of the pipeline in critical water conditions, so the maximum load capacity of the hauling machine must also take this possibility into account, with the result that the hauling machine is grossly oversized for NR operations carried out in normal conditions.
PCT Patent Application No. WO 2006/027189 describes a method which employs gripping assemblies for gripping either the pipeline or the rope connected to the pipeline. Such assemblies, however, are normally only used on J-lay vessels (i.e., for launching the pipeline substantially vertically), and, because they operate discontinuously, may result in uncontrolled slippage of the rope.
A need is therefore felt to enable any type of laying vessel to handle emergency situations when abandoning and recovering the pipeline.